The present disclosure relates to an organic EL (Electro Luminescence) display panel which uses organic EL elements utilizing an electroluminescence phenomenon of organic materials, and to a method of manufacturing the same.
In recent years, as a display panel for use in a display device such as a digital television set, an organic EL display panel having a plurality of organic EL elements arranged in a matrix pattern on a substrate has been put to practical use.
In an organic EL display panel, in general, a light emitting layer of each organic EL element and the adjacent organic EL element are partitioned from each other by an insulating layer formed from an insulating material. In an organic EL display panel for color display, organic EL elements form sub-pixels that emit light in R, G and B colors, individually, and the R, G and B sub-pixels adjacent to one another are combined to form a unit pixel in color display.
The organic EL element has a basic structure in which a light emitting layer containing an organic light emitting material is disposed between a pair of electrodes. At the time of driving, a voltage is impressed between the pair of electrodes, and light is emitted attendant on recombination of holes and electrons injected into the light emitting layer.
An organic EL element of the top emission type has an element structure in which a pixel electrode, organic layers (inclusive of a light emitting layer) and a common electrode are sequentially provided over a substrate. Light from the light emitting layer is reflected by the pixel electrode formed from a light reflecting material, and is emitted upward from the common electrode formed from a light transmitting material. The common electrode is often formed over the whole surface of a display pixel section on the substrate. Attendant on an increase in the size of organic EL display panels for use in larger-sized display devices such as television sets, the electric resistance of the common electrode is increased. At parts far from a current feeding part, therefore, sufficient current supply is not attained, due to a voltage drop, and light emission efficiency is thereby lowered. This may lead to generation of irregularities in luminance
In view of this problem, for example, Japanese Patent Laid-open No. 2002-318556 proposes a technique for lowering the electric resistance of the common electrode. In the technique, an auxiliary electrode layer is extended in the same layer as pixel electrodes on a substrate, and a common electrode is superposed thereon, for achieving electrical connection with the common electrode. In addition, there have been proposed a technique in which an auxiliary electrode layer and a common electrode are stacked on each other through a hole injection layer formed from a metallic oxide in order to achieve electrical connection between the auxiliary electrode layer and the common electrode (see, for example, Japanese Patent No. 5884224), and a technique in which stacking of the layers is conducted through an electron transport layer containing metallic atoms (see, for example, WO 2015/151415).